The invention relates generally to a process for converting magnesium fluoride (MgF.sub.2) to a useable product and more specifically to the conversion of MgF.sub.2 to calcium fluoride (CaF.sub.2) using calcium hydroxide (Ca(OH).sub.2), calcium oxide (CaO) or calcium carbonate (CaCO.sub.3) and is a result of a contract with the United States Department of Energy.
In the reduction of uranium tetrafluoride to uranium metal with magnesium for use at various DOE facilities, large quantities of MgF.sub.2 slag are produced. Presently this magnesium fluoride is processed through one of two routes depending on whether it contains enriched or depleted uranium. If the slag is produced from reduction of enriched uranium it is processed by leaching with nitric acid for uranium solubilization and recovery. The uranium barren slag is neutralized with lime, filtered, placed in drums and eventually dried for long term storage. Some of the magnesium fluoride, from both depleted and enriched uranium, is recycled as liner material for future reductions. The slag from depleted uranium production, when not recycled, is placed in below ground pit storage, but the procedure of burying materials can threaten underground water sources. It is preferred to minimize the amount of slag requiring storage, therefore a project was begun to develop a process converting the magnesium fluoride slag to usable, recyclable and possibly saleable material.
An attempt was made to use the MgF.sub.2 to make anhydrous hydrogen fluoride (HF) but the reaction proved to be very slow and incomplete and resulted in a need for storage of voluminous quantities of magnesium sulfate contaminated with residual uranium. Since anhydrous HF is usually made from CaF.sub.2, investigation were begun to study the possibility of converting MgF.sub.2 to CaF.sub.2 but the literature was not encouraging, Mellor's A Comprehensive Treatise on Inorganic and Theoretical Chemistry specifically states that CaO does not react with MgF.sub.2 ; that MgF.sub.2 is decomposed by alkali carbonates, not mentioning alkaline earth carbonates (such as CaCO.sub.3); and is silent on the use of Ca(OH).sub.2 in such a process. Nevertheless work was begun to see if MgF.sub.2 would be decomposed using CaO, CaCO.sub.3 or Ca(OH).sub.2.